Protective packaging of delicate mechanisms



NOV 15 1956 R. F. HIGH 3,285,400

PROTECTIVE PACKAGING OF DELICATE MECHANISMS Filed May '7, 1965 /lV VEN 70E,

United States Patent() 3,285,400 PROTECTIVE PACKAGING F DELICATE MECHANISMSV Roy F. High, Washington, D.C., assignor to the United States of America as represented by the Secretary of the Army Filed May 7, 1965, Ser. No. 456,895 Claims, (Cl. 206-46) vModern Warfare and space technology require that suicient .ruggedness be designed into' a mechanism so that it will function properly under its operational environment and that it will live through violent transportation and handling situations, severeacceleration forces of launching or ring, and in certa-inapplications enormous deceleration forces generated by impact.

In space exploration .for example, unmanned landings on t-he moon and the nearby planets are contemplated. In such situations it is desirable to place delicate measuring and testing devices on the surface with their own telemetering equipment to relay information thatis gathered after the landing to the earth or orbiting space stations. In certain milita-ry applications, it is necessary to remotely ernplace mines and similar weapons by means of shell, rocket or ballistic missile delivery. The sensing mechanisms, timers and the Ilike used in these weapons .would therefore have to withstand tremendous inertial and gravitational forces prior to their activation.

While it is possible to 'build reliable mechanisms which employ moving parts to withstand these severe conditions, they are impractical because their cost of construction is very high and the devices themselves become extremely heavy.

The most satisfactory solution to this problem is to pot -the arming mechanism or the delicate instrument, to prevent relative movement between its parts before it is transported, in a solid material that can easily be removed just prior to the operation of the device. The potting material must be non-corrosive, `have good dielectric properties, 'be solid over a wide ran-ge of temperatures, specifically in the military storage range of 65 F. to -|-l60 F., have the property of being able to be melted and poured into a cavity containing a delicate device, then solidifying to completely ll the void, and most important, be easily and completely removable from the cavity and from the dev-ice just 'before the device is required to ope-rate.

With the above potting technique, the design of the mechanism need only lbe rugged enough to assure proper Ifunctioning lunder the operational environment, since the ruggedness to survive the transportation, tiring, etc., will be provided by the potting material.

It is therefore an object of this invention to provide a method and material for potting delicate mechanisms so that they will be protected from high g forces before operation.

Another object of the invention is to provide a potting media and method for protecting sensitive devices with a material that is a solid -substance when confined and which will evaporate when released.

of mechanism it is in no way limited thereto.

Patented Nov. 15, 1966 A further object of the instant invention is the provision of a method and material .for the non-permanent potting of delicate mechanisms :having moving parts with a fugitive chemical compound. i.e. one that is likely to evaporate or disappear.

Still a further object of the present invention is to provide a fugitive potting technique that utilizes a chemical compound that is economical to manufacture and is easy to prepare in pure form.

According to the present invention, the foregoing and other objects are attained by position-ing the mechanism to be protected in a container, completely filling the cavity with a molten fugitive potting material that will sublime from the solid to the vapor state, sealing the container and then allowing the potting material to solidify. The potted mechanism is now able to be safely transported to its intended site. When it is desired t-o put the mechanism in operation, the container is opened, the solid potting material sublimes or evaporates and the mechanism is completely free to function in its intended manner.

The specific nature of the invention, as well as other objects, aspects, uses and advantages thereof, will clearly appear from the following description and from the accompanying drawing, in which:

FIG. l is a partial sectional view showing a gear train mechanism potted in accordance with the teachings of this invention; and

FIG. 2 is a partial sectional view showing an alternate means of potting a ldevice according to the instant invention.

v'Referring' now to the drawing and particularly to lFIG. l, there is shown a gear train mechanism 12, completely surrounded Iby a fugitive potting compound 13 and housed within a container or casing 11. Device-12 is shown as being a simple gear train mechanism for ease of explanation purposes only. While the potting method and material of this invention -has special utility with this type Other sensitive devices such as clocks, timers, measuring and testing instruments, triggering mechanisms or the like may vbe potted -in the manner taught by the instant invention. The container 11 which may be a mine or .bomb casing or the shell of a missile is sealed -by suitable means, such as a frangible member L14, and is provided with a means 15 to :break the seal when desired. The pointed striker ymeans 15 provides a simple and convenient arrangement for .breaking the seal, but obviously any other means to break the seal may Ibe employed.

The potting material 13 surrounding the delicate device 12 is denominated a fugitive potting compound Ibecause it is capable of evaporating or disappearing from the solid state directly to the vapor state under certain temperatures and pressure-s. The process by which a chemical composition passes directly from the solid state to the vapor state is commonly termed sublimation. It is absolutely essential that the fugitive potting 13 sublime when the seal is broken in order to assure t-hat the `gear mechanism 12 or other device that is potted is completely free to operate. Also, 1in t'he case of remote-ly emplaced articles as mentioned above, it is necessary that the potting compound ybe self expelling from the casing 11 since the article will be untended at the point of use. The potting compo-und 13 should also sublime lrapidly at standard temperature and pressure because many devices to be potted will ybe 4operated under normal or near norma-l atmospheric conditions and it is often desirable that they rbecome operational in the shortest possible time.

After the rigidly potted mechanism 12 and its casing 13 reach the intended site, `striker 15 is actuated by any suitable means (not shown )to break sea-l 14. Fugitive poti ting 13 willthensublime yanclle'ave the gear trainflZy free to function.

In situations where'it is necessary yto add heat to bring In this embodiment, adelic'ate mechanismZZ: is rigidly.

` is allowed to cool and solidify. The gear train mechanisrn 12 isy now ycompletely, protected from its environpottecl'in ya sublimable vcompoundfiar within a container 21` provided with heating means 27, seal 24 and seal ybreaking means 25. The rneans 27 'for heatingthe fugis c ytive potting is illustrated'for simplicity as consisting of a ls'inipleelectrical circuit having apower supply 28, a switch A29 and heater 3l).l When the seal'Zfll is broken, switch 29,

is closed'to bring about 'the desired heating of the fugitive of will be vassured In order to fully protect sensitivedevices' 12 :and 22 yfrom shockdamage from forcesvas high as 50,000 g and to protect them fromany harmful chemical changes due to the presence of moisture or 'other corrosive agents that could be encountered before they are to rbe activated,the fugitive pottingmust completely surround the devices inpheric conditions and are solids above the top of fthe military storage range of 160 F. or 71 C. as is evident from the above tabulation. These compounds also readily lend themselves to liquid encapsulation under standard atmospheric pressure because their vapor pressures at their melting points are substantially below one atmosphere or 760 mm. Hg, and their boiling points are suiciently above their melting points to allow pouring of the compound in liquid form without virtual boiling. By heating any of these fugitive potting compounds to a temperature slightly above its melting .point it can be easily poured or injected into the container to completely ll the cavity and surround the mechanism. Furthermore, these bi-cyclic compounds are prepared in pure form and therefore their chemical and physical properties or predictable and uniform.

The specific biJcyclic compound that is particularly useful as the fugitive potting material for military purposes is bi-cycloheptane (2,2,1). In addition to having good'pouring qualities vneeded, for feasible liquid encap- `sulation `it has the desirable characteristicsofbeing an f excellent dielectricl material, chemicallyl inert, non-cor rosive and non-toxic, and economical to produce.y

, In the practice of my invention, the delicate device v12 v -to be protected is irst placed or :otherwise positioned 'Within its container 11. A quantity of bi-cycloheptane yas the ,fugitive potting compound 13 is then heated slightly above its melting point and is-pourcdy or injected into yther container until it is completely filled. The container is then closed by sealing means 14 and the bi-cycloheptane ment and it will remain in this safe condition throughout the extreme temperatureconditionsthat itmay ,encounter c within they militaryy storage range. At the point of use,

the; seal 14 is broken -by ystriker means 1S and the fugitive potting sublimesl at'the lambient temperatureand pressure leaving the mechanism 12 free to operate.

described vare only exemplary and that various modiiications ycan be made in construction and arrangement within the, szcoper of the invention as defined yin the appendedv ,f y,

claims. y y y I claim asmy inventionz.

i y(a)v rigidfcasingmeans enclosing said mechanism for cluding their intricate parts, it must completely ll theconr i transporting.said mechanism to its operatingy site, f v v tainer, and it vmust 'remain'fafsolid throughout thel storage '30 (b) said casing being provided withmeans for sealing period; For military applications, to' which this invention vthe interior of said casing from theambient atmosespecially applies, the compound mustl besolid upto i phere vbefore transportation, y f f f F. f w (c) seal-breakingl meanssecured to saidcasin'g, f To accomplishtheabove objectives this invention yutir (d) heating means securedyto said casing, rliz'es abi-cycliccompound as the fugitive pottingzmaterial .3) (e) a sublimable solid potting compound completelyv v12 and 23 vchosen fromy they following group:r occupying the'spacewithin sadcasingnottaken by f saidy mechanismv and yby said seal-breaking means Compound Mening Baumgand by Sad hang means,

' Point-C CJ P01 i CJ .(f). said mechanism being held rigidly in an inoperable f 40 position by said potting compound, and i'cycloheptane (2311 87 105 (g) means for activating said seal-breakinu means and amphor 176 204 D Naphfhmm, sa 22 217, 9 said heating means, thereby causing said pottmg compound to sublime and rendering said mechanism The above compounds will sublime at standard atmos- 45 Operable- 2. Apparatus according to claim 1, said potting compound being chosen from the group of lbi-cyclic compounds of bi-cycloheptane, camphor, and naphthalene.

3. Apparatus according to claim 2 wherein the potting compound is bi-cycloheptane.

4. Apparatus according to claim 2 wherein the potting compound is camphor.

5. Apparatus according to claim 2 wherein the lpotting compound is nahpthalene.

References Cited by the Examiner UNITED STATES PATENTS 2,404,441 7/1946 Hopkins 89-1 2,775,345 12/1956 Pingfey 206-46 X 3,138,100 6/1964 Peschko 206-46 X LOUIS G. MANCENE, Primary Examiner.

MARTHA L. RICE, Examiner.

` ;It will be apparent rthat the yembodimentr shown yand y f v n ,1; Apparatus for f protecting va delicate mechanismy against' adverse environmental :corr1ditions,y comprising: 

1. APPARATUS FOR PROTECTING A DELICATE MECHANISM AGAINST ADVERSE ENVIRONMENTAL CONDITIONS, COMPRISING: (A) RIGID CASING MEANS ENCLOSING SAID MECHANISM FOR TRANSPORTING SAID MECHANISM TO ITS OPERATING SITE, (B) SAID CASING BEING PROVIDED WITH MEANS FOR SEALING THE INTERIOR OF SAID CASING FROM THE AMBIENT ATMOSPHERE BEFORE TRANSPORTATION, (C) SEAL-BREAKING MEANS SECURED TO SAID CASING, (D) HEATING MEANS SECURED TO SAID CASING, (E) A SUBLIMABLE SOLID POTTING COMPOUND COMPLETELY OCCUPYING THE SPACE WITHIN SAID CASING NOT TAKEN BY SAID MECHANISM AND BY SAID SEAL-BREAKING MEANS AND BY SAID HEATING MEANS, (F) SAID MECHANISM BEING HELD RIGIDLY IN AN INOPERABLE POSITION BY SAID POTTING COMPOUND, AND (G) MEANS FOR ACTIVATING SAID SEAL-BREAKING MEANS AND SAID HEATING MEANS, THEREBY CAUSING SAID POTTING COMPOUND TO SUBLIME AND RENDERING SAID MECHANISM OPERABLE. 